Kepler-81 d
Kepler-81 d is a terrestrial planet orbiting Kepler-81 in the constellation Cygnus. It lies about 1,136 light-years from Earth and was discovered in 2014 using the transit method.
How Big Is Kepler-81 d?
Kepler-81 d has a radius of 1.21 times that of Earth.
Is Kepler-81 d in the Habitable Zone?
Kepler-81 d orbits inside the inner edge of the habitable zone of Kepler-81. So close to its star, surface conditions are far too hot for liquid water.
Habitable zone of Kepler-81: 0.289–0.713 AU (conservative: 0.366–0.676 AU), per Kopparapu et al. (2014). Earth orbits the Sun at 1 AU.
See the full interactive habitable-zone view in the Exoplanet Explorer app ›
Orbit and Year Length
A year on Kepler-81 d — one full orbit around Kepler-81 — lasts 20.8 Earth days, shorter than Mercury's 88-day year. It orbits at an average distance of 0.128 AU — closer to its star than Mercury is to the Sun.
How Was Kepler-81 d Discovered?
Kepler-81 d was discovered in 2014 using the transit method, with observations from Kepler.
The transit method watches a star for the tiny, regular dip in brightness that occurs when a planet crosses in front of it. The depth and timing of these dips reveal the planet's size and orbital period.
How Far Away Is Kepler-81 d?
Kepler-81 d is 1,136.0 light-years (348.3 parsecs) from Earth. Light arriving here tonight left the planet about 1,136 years ago. A probe traveling at the speed of Voyager 1 — about 17 km/s, the fastest outbound spacecraft ever launched — would need roughly 19,993,600 years to make the journey.
Earth Similarity Index
The Earth Similarity Index (ESI) scores how physically similar a planet is to Earth, from 0 to 1, based on radius, density, escape velocity and surface temperature. Kepler-81 d scores 0.45, ranking #341 of 5,568 planets with a known ESI. For reference, Mars scores about 0.70.
The Host Star: Kepler-81
Kepler-81
- Surface temperature
- 4,500 K (Sun: 5,772 K)
- Radius
- 0.60 R☉
The Kepler-81 Planetary System
Kepler-81 d is one of 3 known planets in the Kepler-81 system. Its siblings:
- Kepler-81 b (Mini Neptune)
- Kepler-81 c (Mini Neptune)
Kepler-81 d — Complete Data
| Radius | 1.210 Earth radii (0.108 Jupiter radii) |
|---|---|
| Orbital period | 20.84 days |
| Orbital distance | 0.128 AU |
| Earth Similarity Index | 0.45 |
| Distance from Earth | 1,136.0 light-years (348.3 parsecs) |
| Constellation | Cygnus |
| Discovery method | Transit |
| Discovery facility | Kepler |
| Discovery year | 2014 |
Data: NASA Exoplanet Archive, last updated 2014-05-14. Earth Similarity Index: PHL @ UPR Arecibo.
Frequently Asked Questions About Kepler-81 d
Is Kepler-81 d habitable?
No — Kepler-81 d orbits too close to its star and is too hot for liquid water to exist on its surface.
How far away is Kepler-81 d?
Kepler-81 d is about 1,136 light-years from Earth in the constellation Cygnus. A spacecraft traveling as fast as Voyager 1 (about 17 km/s) would need roughly 19,993,600 years to get there.
How big is Kepler-81 d compared to Earth?
Kepler-81 d has 1.21 times the radius of Earth.
How long is a year on Kepler-81 d?
One orbit around Kepler-81 takes 20.8 Earth days — short enough that 18 of its years would fit into one Earth year.
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